Atomic-scale structural evolution of Ge(100) surfaces etched by H and D

Abstract

The atomic-scale structural evolution of Ge͑100͒ surfaces etched by H͑g͒ and D͑g͒ at T s ϭ400 K is studied using scanning tunneling microcopy ͑STM͒ and field emission-scanning electron microscopy ͑FE-SEM͒. The STM investigation reveals that etching of the Ge͑100͒ by H͑g͒ and D͑g͒ proceeds initially via the production of single atom vacancies ͑SV͒, dimer vacancies ͑DV͒, and subsequently, line defects along the Ge dimer rows. It is also observed that D͑g͒ etches the Ge͑100͒ surface eight times faster than H͑g͒ does. After extensive exposures of the surface to H͑g͒, the FE-SEM images show square etch pits with V-groove shapes, indicating that H͑g͒ etching of the Ge͑100͒ surface proceeds anisotropically.

Surface Reactions of Atomic Hydrogen with Ge(100) in Comparison with Si(100)

“…Both the interatomic distances on the surface (labelled A and B in the Figure 1) and the lattice constant are larger by ~4% Displayed in Figure 2 is a series of low-dose H 2 TPD spectra taken from the Ge(100)-2 × 1 surface pre-exposed to indicated H(g) exposures (ML) at 300 K. The redcolored desorption curves are those with an additional shoulder peak (labelled β 2 at 520 K) indicative of dihydrides, GeH 2 (a), which grows beyond the primary peak (β 1 at 570 K) for monohydrides, GeH(a). Similar double-peaked desorption behaviors have been reported for both Si(100) [8][9][10][11][12] and Ge(100) surfaces [8][9][10][11][12][16][17][18][19][27][28]. However, there is one distinct aspect observed here: the β 2 -peak grew, albeit relatively slowly compared with Si(100), well beyond the 1.33-ML H(a) coverage corresponding to a (3 × 1):H phase on Ge(100) (see Figure 3).…”

“…We thus conclude that H(g) atoms, when exposed to Ge(100) at T s below 300 K, not only form surface GeH x (a) (x > 1) species but also abstract GeH 3 (a) to produce the gaseous etch product GeH 4 from Ge(100) during H(g) dose. A very similar behavior was observed on Si(100), although the threshold T s is about 200 K lower on Ge(100) [8][9][10][11][16][17][18]31]. It should be noted that the β 2 -H 2 peak grows at the sacrifice of the β 1 -H 2 peak with decreasing T s : The β 1 -peak intensity decreased by ~33% when T ads decreased from 450 K to 120 K. This suggests that the increase of the total H 2 desorption with decreasing T ads was due to the increased concentration of increased diand tri-hydrides on the surface, rather than to etchinginduced roughening and a subsequent increase in the area of the surface.…”

“…It has been well established that both Si(100) and Ge(100) surfaces reconstruct to make (2Í1) surfaces, on which each surface atom has only one dangling bond. Such dangling bonds are readily passivated by H(g) with a nearly unity sticking probability, leading to well-ordered monohydride-saturated surfaces, Si(100)-2 × 1:H [8][9][10][11][12] and Ge(100)-2 × 1:H [16][17][18][19][27][28]. Schematic views of the unit cell of a diamond crystal lattice and the (100)-2 × 1:H surface are drawn in Figure 1.…”

“…On the other hand, much less research attention has been paid to the surface chemistry of H(g) on Ge(100) compared with Si(100) [15][16][17][18][19]. While germanium attracts renewed attention in view of the next-generation semiconductor technology due to its high carrier mobility [20][21][22][23][24][25][26][27][28][29][30], we decided to perform a comparative study on the H(g)/ Ge(100) system.…”

Quantitative coverage and stability of hydrogen-passivation layers on HF-etched Si(1−x)Gex surfaces

“…After exposure of Si and Ge surfaces to large doses of atomic hydrogen, etch pits have sometimes been observed to develop in small areal densities. 43 Such pits are usually confined by facets with ͑111͒ orientation of lowest surface energy. HF etching, however, will predominantly terminate ͑111͒ terraces with SiH monohydride, the vibrational stretching amplitude of which being aligned perpendicular to the ͑111͒ surface.…”